Conventional magnetic field-based current sensors generally include a magnetic field sensor, an iron core, and an amplifier. The iron core surrounds an electrical conductor, generally comprising copper for carrying the current to be measured, the current to be measured resulting in a magnetic field generated in the iron core. The magnetic field sensor is arranged in a gap in the iron core. Thus, the field lines of the magnetic field induced in the iron core by the current to be measured pass through the magnetic field sensor. The magnetic field sensor generates an electrical output signal generally proportional to the current to be measured, and this signal is amplified by an amplifier, such as an operational amplifier.
The iron core in conventional current sensors primarily provides two functions. First, the conducting of the magnetic field induced by the current to be measured through the magnetic field sensor, and second, the screening of the magnetic field sensor from extraneous electric and magnetic fields which are known to cause measurement error. However, the use of iron cores results in a sensor cost that is often too expensive for many applications.
Some lower cost current sensors are known which dispense with the need for an iron core. However, such sensors generally do not provide sufficiently accurate primary current measurement, nor do they generally provide sufficient linearity (between the current to be measured flowing as primary current and the magnetic flux reaching the magnetic sensor).
For example, certain automobile current sensing applications are known to require precise measurement of electric current, such as for the control of motor and phase current in the electronic drive system. Small sensor size is also required based on the need to measure current directly on a printed circuit board. Moreover, low cost is also required in these automotive applications and other high volume applications. What is needed is a new current sensor design that provides improved sensor performance while also providing low cost.